Calculate flood irrigation water volume in acre-feet and gallons from irrigated area and application depth. Plan water deliveries accurately.
Flood irrigation applies water across the soil surface in a controlled sheet or ponded basin. The volume of water needed depends on the area to be irrigated and the target application depth. Expressing this volume in acre-feet and gallons lets you coordinate with water districts, size conveyance structures, and plan pump run times.
One acre-foot equals 325,851 gallons — the volume of water required to cover one acre to a depth of one foot. One acre-inch (1/12 of an acre-foot) equals 27,154 gallons. These conversions are fundamental to irrigation water budgeting.
This calculator converts your irrigated area and depth into volume in acre-feet, acre-inches, and gallons, helping you plan water orders, pump scheduling, and water-rights accounting. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Water districts deliver and meter water in acre-feet. Knowing the exact volume for each irrigation helps you stay within your allocation, time water orders correctly, and avoid over- or under-watering. Having a precise figure at your fingertips empowers better planning and more confident decisions. Manual calculations are error-prone and time-consuming; this tool delivers verified results in seconds so you can focus on strategy.
Volume (ac-ft) = Area (ac) × Depth (in) / 12 Volume (gal) = Volume (ac-ft) × 325,851 Volume (ac-in) = Area (ac) × Depth (in)
Result: Volume = 13.33 ac-ft = 4,344,680 gal
40 acres × 4 inches / 12 = 13.33 ac-ft. Converting: 13.33 × 325,851 = 4,344,680 gallons. This is the gross volume the pump or canal must deliver for one irrigation event.
Flood irrigation encompasses several methods: basin flooding (ponded), border strips (long narrow strips), and furrow irrigation (water in channels between rows). All share the fundamental volume relationship of area times depth.
Laser-leveling fields dramatically improves uniformity, raising efficiency from 40% to 60–70%. Surge flow irrigation alternates water on and off to the furrow, reducing deep percolation. Poly-pipe with gated outlets provides more uniform inflow than head ditches.
In the western U.S., water rights are often expressed in acre-feet per year. Knowing the volume for each irrigation event and tracking cumulative use ensures compliance and avoids penalties for over-pumping or exceeding surface-water diversions.
An acre-foot is the volume of water that covers one acre to a depth of one foot. It equals 325,851 gallons or 43,560 cubic feet.
An acre-inch is 1/12 of an acre-foot (27,154 gallons). Irrigation depths are often expressed in inches, while water allocations and reservoir sizing use acre-feet.
Divide the net depth needed by the flood efficiency (typically 0.50–0.65) to get the gross depth. Then use the gross depth in this calculator to determine total volume.
Duration depends on supply flow rate: Time (hrs) = Volume (gal) / (Flow GPM × 60). A 40-acre set at 4 inches with a 2,000 GPM supply takes about 36 hours.
Yes. The volume calculation is the same for any surface irrigation method. The difference is in the field layout and how water is distributed, not in the total volume required.
Districts use weirs, flumes, or ultrasonic meters at turnouts. Flow is measured in cubic feet per second (CFS) and volume in acre-feet. 1 CFS flowing for 1 day ≈ 2 ac-ft.